1. Field of the Invention
The invention refers to a coupling device having two coupling members and clamping means for axially clamping both coupling members. At least three prismatic pins project from the first coupling member each of which is provided with a prismatic surface at at least on side thereof. At least three circumferentially spaced z-reference surfaces are formed from the first coupling member which extend within an x-y-plane which is perpendicular to the clamping direction. The second coupling member comprises at least three grooves in a circumferential position corresponding to the circumferential arrangement of the prismatic pins. Axially elastic elements are provided at the grooves for a precise positioning of the coupling members relative to each other within the x-y-plane.
2. Description of Related Art
A clamping device is disclosed in the document EP-A-255 042 (=U.S. Pat. No. 4,855,558) wherein one of both coupling members is provided with a plurality of projecting posts. For a precise positioning of both coupling members relative to each other in z-direction the free end surfaces of the posts are formed as z-reference surfaces. A corresponding plurality of z-counter reference surfaces are formed on the other coupling member in an arrangement corresponding to the arrangement of the posts. All z-counter references extend within a common plane and cooperate with the z-reference upon clamping. A different arrangement for positioning two coupling members in z-direction is disclosed in German utility model 295 21 030 (=U.S. Pat. No. 5,791,803).
The invention is based on the problem to improve the means for positioning both coupling members in z-direction.
To this end the above-mentioned coupling device has one coupling member provided with prismatic pins, the free end surfaces of which are formed as z-reference surfaces. The second coupling member is formed with grooves which are arranged in correspondence to the position of the prismatic pins. The base of each groove is provided with a z-counter reference surface adapted to cooperate with one of the z-reference surfaces during clamping of both coupling members. All z-counter reference surfaces extend within a common plane. Thus, according to the invention the prismatic pins are utilized firstly for providing proper references serving for angular adjustment of the second removable coupling member with respect to the first coupling member, and secondly for providing z-reference surfaces for allowing precise z-positioning of both coupling members. Correspondingly, the grooves in the second coupling member serve firstly for proper angular positioning the second coupling member with respect to the first one and secondly for creating proper z-counter reference surfaces. Thus, the invention allows for omitting separate posts or similar means from one of the coupling members for positioning the coupling members in z-direction. Moreover, the invention allows for obtaining a very high precision of positioning one coupling member with respect to the other coupling member in angular direction and z-direction even if both coupling members are very often separated (unclamped) and again clamped.
Preferably the z-counter reference surfaces are formed upon a vertical projection from the base of each groove. In cases where each groove includes an insert of general U-shaped configuration the basic part of which is mounted to the projection for allowing the prismatic pin to enter the insert during clamping the center of the basic part may be formed to a z-counter reference surface. Alternatively the projection may extend upwardly over the basic part for being formed with the z-counter reference surface.
The invention is of specific relevance when working on a workpiece which is mounted to the movable coupling member whereas the other coupling member may be fixedly mounted to the head of a machine tool. In such cases normally only a small exterior axial force is acting upon the clamped coupling members. However, there are different possibilities of utilizing the coupling devices according to the invention wherein the clamped coupling members are subjected to a substantial axial load. Such a situation is encountered for example when producing a die-pressed part from metal powder wherein a first coupling device is connected in between a movable press ram and a first die associated to the press ram, and a second coupling device is connected in between a counter support and a second fixed die. The substantial pressing force which has to be applied for pressing the metal powder which is within both dies to the desired die moulded part acts upon the clamped coupling members in the direction of the clamping force developed by the clamping means. The precision of the z-positioning of both coupling members may be impaired by a pressing force exceeding a given threshold value.
For securing the precision of the z-positioning under very high axial load on the clamped coupling members an embodiment of the invention provides for a plurality of circumferentially spaced posts on one coupling member, each post having at its free end an additional z-reference surface, and for providing additional z-counter reference surfaces on the other coupling member which are arranged in correspondence to the additional z-reference surfaces.
Thereby, the solidity of the z-positioning is increased because the outer load is devided among a greater surface formed by the reference surfaces altogether. Preferably, the additional z-counter reference surfaces are made on the upper side of the coupling member supporting a die.
If the precision of the z-positioning is not of very high relevance an embodiment of the invention may be made such that between each additional z-reference surface and each associated additional z-counter reference surface a distance of one or a few xcexcm is left when both coupling members are clamped, i.e. the z-counter reference surfaces abut the z-reference surfaces. When the axial load should be minor only the z-reference surfaces and the z-counter reference surfaces cooperate for z-positioning. If the load will be high the additional z-counter reference surfaces will engage the additional z-reference surfaces. However, the invention may be carried out also in such a way that in case of minor load only the additional z-counter reference surfaces abut the additional z-reference surfaces and a short distance may be left between the z-counter reference surface and the z-reference surface when both coupling members are clamped. The last mentioned embodiment of the invention is advantageous therein that any deformation of the posts caused by high load has no influence on the adjustment of the coupling members with respect to each other within the x-y-plane.
Further preferred embodiments of the invention are identified in the sub-claims.